Pyridine-2,3-dicarboxylc acids and esters are building blocks for numerous bio-active products, particularly imidazolinone herbicides, for example U.S. Pat. No. 4,758,667. Known methods to prepare pyridine-2,3-dicarboxylate derivatives via the oxidation of a suitable quinoline or alkylpyridine precursor are often plagued by the use of costly oxidants such as KMnO.sub.4, H.sub.2 Cr.sub.2 O.sub.7, SeO.sub.2 and the like; by long reaction time cycles such as in the use of ozone, electrolysis and the like; and by undesirable side reactions such as decarboxylation, N-oxide formation and the like. Therefore, new methods to construct the desired pyridine dicarboxylate product are continually being sought.
It has now been found that a rapid one vessel process to prepare a pyridine-2,3-dicarboxylate derivative is readily obtained via the sequential condensation of the appropriate alkyl vinyl ether with Vilsmeier reagent, oxalacetate and an ammonia source.